Improved nitrogen fertilizer management reduces nitrous oxide emissions in a northern Prairie cropland.

Arable croplands are a significant source of nitrous oxide (NO) emissions, largely due to nitrogen (N) fertilizer applications to support crop production. Nevertheless, there is limited research on the NO dynamics from canola-wheat rotations in the semi-arid northern Prairies, an important agricultural region. Here, we present micrometeorological NO fluxes measured from January 2021 to April 2024 in Saskatchewan, Canada, to evaluate the impact of N fertilizer management on the year-round NO emissions from a canola-wheat rotation. A combination of two 4R (Right Source, Right Rate, Right Time, Right Place) N management practices - a reduced N rate and an enhanced efficiency N fertilizer source - was compared to common fertilizer management practices for the region. Two periods at high risk for NO flux events were identified, after N fertilizer applications and the following spring thaw, with the magnitude of emissions varying over the multi-year period. As for cumulative emissions, the growing season (GS) NO emissions were 50 % of annual emissions, presenting an opportunity to mitigate NO emissions through improved N fertilizer management. Indeed, the improved 4R N management reduced NO emissions by 57 % over the entire study period without impacting yields. The reduction in GS NO emissions resulted from the 4R N management lowering mean NO flux at times of high WFPS (>50 %). The non-growing season (NGS) NO accounted for 11-67 % of annual emissions. Fall soil nitrate levels were a strong explanatory variable of NGS emissions (r = 0.69, r = 0.39), but the rate of change and magnitude of NGS emissions depended on thawing conditions - lower for drier thaws, higher for wetter thaws. Ultimately, better N fertilizer management reduces cumulative NO emissions from cropping systems when practiced for several years.